U.S. patent number 6,028,143 [Application Number 09/189,340] was granted by the patent office on 2000-02-22 for rubber composition containing cross linkable polyethylene.
This patent grant is currently assigned to Bridgestone Corporation. Invention is credited to Uchu Mukai.
United States Patent |
6,028,143 |
Mukai |
February 22, 2000 |
Rubber composition containing cross linkable polyethylene
Abstract
The present invention provides a rubber composition in which the
coexistence of low heat build-up, heat resistance and high hardness
can be achieved without damaging failure characteristics. According
to the present invention, a rubber composition comprising a 100
parts by weight of matrix rubber and a 2-75 parts by weight of a
polyethylene composition which contains 0-80% by weight of
polyethylene and 20% by weight or more of a composite comprising a
polyethylene component and a rubber component previously bonded via
a coupling agent to the polyethylene component, said rubber
component is crosslinked with the matrix rubber. At least at one of
the kneading stages before the final stage, the compound is kneaded
so that the maximum temperature of the compound of the kneading of
that stage is higher than the melting point of the polyethylene
component mixed, preferably, by 10.degree. C. or more.
Inventors: |
Mukai; Uchu (Kodaira,
JP) |
Assignee: |
Bridgestone Corporation (Tokyo,
JP)
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Family
ID: |
26459165 |
Appl.
No.: |
09/189,340 |
Filed: |
November 10, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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855038 |
May 13, 1997 |
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Foreign Application Priority Data
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May 16, 1996 [JP] |
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8-121915 |
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Current U.S.
Class: |
525/232; 525/192;
525/193; 525/194; 525/197; 525/240 |
Current CPC
Class: |
C08L
21/00 (20130101); C08L 21/00 (20130101); C08L
2666/06 (20130101) |
Current International
Class: |
C08L
21/00 (20060101); C08L 023/00 () |
Field of
Search: |
;525/240,192,193,194,197,232 |
References Cited
[Referenced By]
U.S. Patent Documents
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4005054 |
January 1977 |
Bonnefon et al. |
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Other References
Shinichi et al., "Polymer Alloy Composition and Its Production",
Patent Abstracts of Japan, vol. 013, No. 595 (C-672, Dec. 27,
1989). .
Mitsuru et al., "Pneumatic Tire", Patent Abstracts of Japan, vol.
016, No. 400 (C-0977), Aug. 25, 1992..
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Primary Examiner: Warzel; Mark L.
Attorney, Agent or Firm: Fish & Richardson P.C.
Parent Case Text
The present application is a continuation-in-part of U.S.
application Ser. No. 08/855,038 filed on May 13, 1997 now
abandoned, which claims priority under .sctn.119 of Japanese Patent
Application No. 121915/1996, filed May 16, 1996, the disclosure of
which is incorporated herein by reference in its entirety.
Claims
What is claimed is:
1. A rubber composition, comprising:
100 parts by weight of a matrix rubber; and
2-75 parts by weight of a polyethylene composition which contains
0-80% by weight of polyethylene and 20% by weight or more of a
composite, comprising
a polyethylene component; and
a rubber component previously bonded via a coupling agent to the
polyethylene component,
wherein the rubber component is crosslinked with the matrix
rubber.
2. The rubber composition of claim 1, wherein the composite
contains about 35-100% by weight of the polyethylene component.
3. The rubber composition of claim 1 or 2, wherein the polyethylene
component is a high density polyethylene.
4. The rubber composition of claim 1 or 2, wherein the rubber
composition is prepared through kneading at a temperature which is
higher by about 10.degree. C. or more than the melting point of the
composite.
5. The rubber composition of claim 1 or 2, wherein the rubber
composition is prepared through several kneading stages in which
the rubber composition is kneaded at least once prior to a final
stage so that the maximum temperature of the kneaded rubber
composition is higher than the melting point of the mixed
composite.
6. A rubber composition, comprising:
100 parts by weight of a matrix rubber; and
2-75 parts by weight of a polyethylene composition which contains
0-80% by weight of polyethylene and 20% by weight or more of a
composite, comprising
a polyethylene component; and
a rubber component previously bonded via a coupling agent to the
polyethylene component,
wherein the rubber component is crosslinked with the matrix rubber
and wherein the rubber composition is prepared through kneading at
a temperature which is higher by about 10.degree. C. or more than
the melting point of the composite.
7. A rubber composition, comprising:
100 parts by weight of a matrix rubber; and
2-75 parts by weight of a polyethylene composition which contains
0-80% by weight of polyethylene and 20% by weight or more of a
composite, comprising
a polyethylene component; and
a rubber component previously bonded via a coupling agent to the
polyethylene component,
wherein the rubber component is crosslinked with the matrix rubber
and wherein the rubber composition is prepared through several
kneading stages in which the rubber composition is kneaded at least
once prior to a final stage so that the maximum temperature of the
kneaded rubber composition is higher than the melting point of the
mixed composite.
Description
FIELD OF THE INVENTION
The present invention relates to a rubber composition suitable for
tires, rubber vibration insulators, and the like.
BACKGROUND OF THE INVENTION
As one of the properties required for the tread of tires, cut
resistance is given. This property is especially important when
tires are used on roads in bad condition, construction sites or the
like which are likely to give visible injuries to tires. As a
direction toward the improvement of the cut resistance of tread, to
improve the hardness of rubber composition and, at the same time,
to make the elongation at break larger have been believed to be
effective. For improving the hardness of rubber composition,
techniques may be considered in which the crosslinking density is
increased by mixing carbon black at a high ratio, increasing the
content of sulfur, or the like.
According to these techniques, however, the elongation at break is
decreased and there occurs a phenomenon called chipping, i.e.,
rubber chips come off from a tire. In order to improve this
property, various tests such as the use of a thermoplastic resin, a
thermosetting resin, etc. have been made. However, these attempts
often have not been able to achieve a desirable result in other
properties, particularly in heat resistance and heat build-up.
Thus, sufficient effects have not necessarily been obtained. For
example, as seen in Japanese Unexamined Patent Publication No.
48-38338, the compatibility of cut resistance and heat build-up was
achieved, but durability and heat resistance were not
sufficient.
Not only in the tread of tires but also in other portions of tires,
it is important to allow high hardness, heat resistance and low
heat build-up to coexist. However, it is an extremely difficult
assignment to achieve.
In rubber products other than tires, the coexistence of high
hardness and low heat build-up is also required, for example, for
rubber vibration insulators, particularly, a rubber for the
suspension of vehicles.
As specific examples of pneumatic tires in which polyethylene is
mixed, U.S. Pat. No. 4,675,349 and U.S. Pat. No. 5,341,863 are
given. The former is characterized by mixing a polyethylene having
a softening point of 35.degree. C. or above at a temperature lower
than that. In this case, inevitably, the polyethylene should be
added in the form of fine particles. Such a polyethylene is
difficult to handle at the time of mixing. Furthermore, when mixed,
polyethylene particles may aggregate to thereby worsen the physical
properties of the resultant compound. The latter is characterized
by using LDPE (low density polyethylene) of which the melting point
of the crystal falls within a range of 104-115.degree. C. In this
case, changes in the physical properties of the resultant rubber
composition are drastic at a high temperature, as described later
in the description of the present invention. Therefore, the latter
composition should be said difficult to use, in particular, as a
rubber composition for tires.
Japanese Unexamined Patent Publication No. 7-266454 discloses a
pneumatic tire in which LDPE or LLDPE (linear low density
polyethylene) is mixed. In this case, changes in the physical
properties of the resultant rubber composition are also drastic at
a high temperature, and this composition should be said difficult
to use, in particular, as a rubber composition for tires.
Generally, when a polyethylene having a low melting point is used,
permanent set in fatigue attributable to the creep of the
polyethylene is observed in the resultant rubber composition in
addition to the above-mentioned problems. Thus, the use of such a
polyethylene is not appropriate.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide a rubber
composition in which the coexistence of low heat build-up, heat
resistance, high hardness and resistance to the permanent set can
be achieved without damaging failure characteristics.
In order to allow low heat build-up, heat resistance, high hardness
and resistance to the permanent set to coexist in a rubber
composition, a material (polyethylene in the present invention) to
be mixed with the matrix rubber composition has to satisfy the
following four essential conditions:
(1) Having a high affinity with the matrix rubber. This influences
on basic reinforcing properties and heat build-up.
(2) Having an elastic modulus by far higher than that of matrix
rubber composition. This influences on hardness.
(3) Being unsusceptible to phase transition and various chemical
reactions at a temperature within the range of usual use.
(4) Not deformed plastically against a minute input. This
influences on resistance to the permanent set.
Focusing the attention on the essential conditions described above,
the present inventor has made intensive and extensive researches on
the blending of various polyethylene resins with rubber. As a
result, the inventor has found a rubber composition in which the
properties described above coexist. Thus, the present invention has
been achieved.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the relationship between bending rigidity and melting
point of polyethylene.
FIG. 2 shows the relationship between bending rigidity and density
of polyethylene.
DETAILED DESCRIPTION OF THE INVENTION
The rubber composition of the invention relates to a rubber
composition comprising 100 parts by weight of a matrix rubber and
2-75 parts by weight of a polyethylene composition which contains
0-80% by weight of polyethylene and 20% by weight or more of a
composite comprising a polyethylene component and a rubber
component previously bonded via a coupling agent to the
polyethylene component, said rubber component is crosslinked with
the matrix rubber. The polyethylene component used in the composite
is preferable a high density polyethylene. Further, when the rubber
composition is kneaded through several stages in the preparation,
the rubber composition is characterized by being kneaded at least
at one of the stages before the final stage so that the maximum
temperature of the kneaded composition of said stage is higher than
the melting point of the polyethylene component mixed therein
preferably by 10.degree. C. or more.
In the present invention, high density polyethylene has a density
of 0.94 or more, and polyethylene with a density of less than 0.94
is described as low density.
The amount of a polyethylene resin component to be mixed should be
2-75 weight parts relative to 100 weight parts of the rubber
component of the composition. When the amount is less than 2 weight
parts, no clear difference is observed and the effect of the
invention is not achieved. When the amount is more than 75 weight
parts, the characteristics as a rubber composition are lost and,
especially, fatigue properties, such as breaking life against
repeated strain, become worse.
Twenty percent by weight or more of the polyethylene composition to
be added should be a composite comprising polyethylene component
previously bonded via a coupling agent to a rubber component. Since
sufficient resistance to the permanent set cannot be obtained if
only a non-crosslinkable high density polyethylene has been added,
it is necessary to inhibit plastic deformation by crosslinking to
some extent the non-crystalline portion of the polyethylene in
order to overcome this problem. Although the physical property of a
rubber composition can be sufficiently improved by using a
polyethylene which has been already crosslinked, the polyethylene
should be added and mixed in the form of fine particles in this
case in order to improve the dispersibility, which is not desirable
in view of processability. Preferably, a high density polyethylene
which undergoes crosslinking after being sufficiently dispersed in
a matrix rubber is used.
The ratio of the composite comprising polyethylene component
previously bonded via a coupling agent to a rubber component has
been set at 20% by weight, or more preferably, 35-100% by weight
because the effect is small if the ratio is less than 20% by weight
to the total polyethylene and the improvement of physical
properties become remarkable if the ratio is 35% by weight or more.
In addition, the ratio of the composite in the polyethylene mixture
is preferably 50% by weight or more, more preferably 80% by weight
or more. When a polyethylene contains 35-100% by weight of a
composite previously bonded via a coupling agent, the effect of the
improvement of physical properties is most remarkable.
The rubber composition is prepared through kneading at a
temperature which is higher than the melting point of the
composite, preferably, by 10.degree. C. or more. The ratio of the
polyethylene component and the rubber component in the composite
ranges preferably from 100/100 to 100/50. Kneading is performed
through several stages. It is preferred that at least at one stage
of these stages before the final stage the maximum temperature of
the kneaded composition be higher than the melting point of the
composite mixed therein, preferably, by 10.degree. C. or more. If
kneaded at a lower temperature than the melting point of
polyethylene, the viscosity of the polyethylene will be high and,
as a result, the dispersibility of the polyethylene and the
affinity thereof with the matrix rubber will be insufficient. These
may result in a deterioration in the breaking characteristics of
the resultant rubber composition.
As the matrix rubber component to be used in the rubber composition
of the invention, diene rubbers such as natural rubber (NR),
polyisoprene rubber (IR), polybutadiene rubber (BR) or
styrenebutadiene copolymer (SBR) may be used independently or in
combination. When the matrix rubber contains natural rubber or
polyisoprene, the effect of the rubber composition of the invention
becomes maximum.
As the rubber component used in the composite, similar to the
matrix rubber component, diene rubbers such as natural rubber,
polyisoprene rubber, polybutadiene rubber or styrene-butadiene
copolymer (SRB) may be used independently or in combination, and
natural rubber is particularly preferable. The coupling agent that
can be used is a usual silane coupling agent, particularly
preferably is .gamma.-methacryloxy propyl trimethoxy silane.
Needless to say, appropriate amounts of conventional additives
including a filler such as carbon black, silica; a softener such as
aromatic oil, spindle oil; an anti-oxidant; a vulcanizing agent; a
vulcanization accelerator; and a vulcanization activator may be
suitably added to the rubber composition of the invention.
PREFERRED EMBODIMENTS OF THE INVENTION
Hereinbelow, the present invention will be described in more detail
with reference to the following Examples and Comparative Examples.
The present invention, however, is not limited to these
Examples.
Rubber compositions were prepared using various polyethylene resins
shown in Table 1 according to the mixing recipes shown in Tables 2
and 3. Each of the compositions was mixed and kneaded using a 250
ml LABO PLASTOMILL (manufactured by Toyoseiki Co.) and with 3 inch
rolls. The mixing and kneading process consisted of two stages.
At the first stage, chemicals excluding those which greatly
influence upon the crosslinking of the matrix rubber at a high
temperature (e.g., a vulcanizing agent, vulcanization accelerator,
and vulcanization activator), rubber component, polyethylene,
carbon black and the like were added. At the second stage,
chemicals and the like which were not added at the first stage were
added and kneaded at a lower temperature than that of the first
stage, .gamma.-methacryloxy propyl trimethoxy silane was used as
the coupling agent.
Then, the resultant composition was vulcanized and various
measurements were carried out according to the methods described
below The vulcanizing conditions were at 145.degree. C. and for 30
minutes. The results are shown in Table 4.
(1) Characteristics of Polyethylene
(a) Measurement of melting point (Tm)
The melting point (Tm) of a polyethylene was measured with a
differential scanning calorimeter (Model DSC200 manufactured by
Seiko Electronics Industry) at a nitrogen flow rate of 20 ml/min
for the range from 20.degree. C. to 180.degree. C. at a heating
rate of 10.degree. C./min. The melting point was defined as a
temperature at which an endothermic peak converge.
(b) Measurement of melt flow rate
The measurement was conducted based on JIS K6760-1981.
(c) Bending rigidity
The measurement was conducted based on JIS K6760-1981 with an Olsen
flow tester.
(2) Measurement of the Temperature of a Compound
The maximum temperature of the rubber compound of the first stage
of kneading was measured using a thermocouple provided at the
mill.
(3) Various Physical Properties of a Rubber Composition
(a) Measurement of hardness
Based on JIS K6301-1995, the spring type hardness (type A) was
measured at 25C.
(b) Tensile strength, at the time of breaking (Tb)
The measurement was based on JIS K6301-1995.
(c) Elongation at the time of breaking (Eb)
The measurement was based on JIS K6301-1995.
(d) Method for measuring permanent set
A vulcanized rubber sample of a dumbbell shape was deformed to 400%
at 25.degree. C. under tension mode at a rate of strain of 12.5%
per second. Then, the load was removed and after 24 hours the
length of the sample was measured. The permanent set was calculated
by the formula given below. The reciprocal of the thus calculated
values were reduced to index numbers in which the value for
Comparative Example 1 is 100. This means that the greater the index
number, the smaller the permanent set. Permanent set (%)=(The
length of the sample after the removal of the load/The original
length of the sample as cut off from the rubber
sheet).times.100.
(e) Hysteresis loss characteristics
Using a dynamic mechanical analyzer manufactured by Rheometrics
Corp., U.S.A., Tan .delta. was measured after giving a sample a
dynamic oscillation strain (amplitude: 1.0%; frequency: 15 Hz) at
50.degree. C. The reciprocal of thus measured values were reduced
to index numbers in which the value for Comparative Example 1 is
100. Accordingly, the greater the index number, the less the
hysteresis loss and the lower the heat build-up.
TABLE 1 ______________________________________ Characteristics of
Polyethylene Resins A B C D ______________________________________
Melting point (.degree. C.) 136 108 124 136 Density 0.964 0.920
0.923 0.958 Bending rigidity 12,500 1,550 2,700 12,000
(kg/cm.sup.2) ______________________________________ A. High
density polyethylene (Mitsubishi Chemical, Product Name: HJ560) B.
Low density polyethylene (Mitsubishi Chemical, Product Name: HE30)
C. Linear low density polyethylene (Mitsubishi Chemical, Product
Name: UF340) D. Silane crosslinking polymer (Mitsubishi Chemical,
Product Name Linklon HF700N)
Component A in Table 1, is a general-purpose polyethylene and is a
high density polyethylene composite consisting of 100% composite
(Mitsubishi Chemical, Product Name: HJ560). The rubber:polyethylene
ratio in the composite is 100:75.
TABLE 2 ______________________________________ Weight part
______________________________________ Matrix rubber*.sup.1 100
Polyethylene variable Carbon black (N330) 50 Aromatic oil 3 Steric
acid 2 Anti-oxidant 6C*.sup.2 1 Zinc oxide 3 Vulcanization
accelerator DPG*.sup.3 0.5 Vulcanization accelerator DM*.sup.4 0.6
Sulfur 1.5 ______________________________________ *.sup.1 IR200,
SBR1500 and BR01 (Japan Synthetic Rubber Co., Ltd.) were used
independently or in combination. *.sup.2
N(1,3-dimethylbutyl)-Nphenyl-p-phenylenediamine *.sup.3
Diphenylquanidine *.sup.4 Dibenzathiazyldisulfide
TABLE 3
__________________________________________________________________________
Temp. Polyethylene IR2200 SBR1500 BR01 C/B (.degree. C.) Kind
Amount (phr)
__________________________________________________________________________
Comparative Example 1 100 0 0 50 150 -- 0 Comparative Example 2 50
50 0 50 150 -- 0 Comparative Example 3 50 0 50 50 150 -- 0
Comparative Example 4 100 0 0 50 155 A 2 Comparative Example 5 100
0 0 50 155 A 10 Comparative Example 6 100 0 0 50 155 A D 0.5 0.5
Example 1 100 0 0 50 155 A D 1 1 Example 2 100 0 0 50 155 A D 8 2
Example 3 100 0 0 50 155 A D 7 3 Example 4 100 0 0 50 155 A D 6.5
3.5 Example 5 100 0 0 50 155 A D 5 5 Example 6 100 0 0 50 155 A D 3
7 Example 7 100 0 0 50 155 A D 0 10 Comparative Example 7 100 0 0
50 155 A D 40 40 Comparative Example 8 100 0 0 50 155 B 10
Comparative Example 9 100 0 0 50 155 C 10 Comparative Example 10
100 0 0 50 155 B D 5 5 Comparative Example 11 100 0 0 50 155 C D 5
5 Example 8 50 50 0 50 155 A D 5 5 Example 9 50 0 50 50 155 A D 5 5
Example 10 100 0 0 45 155 A D 5 5 Example 11 100 0 0 50 145 A D 5 5
Comparative Example 12 100 0 0 50 155 A 75 Example 12 100 0 0 50
155 A D 40 35
__________________________________________________________________________
(In the above Table, "Temperature" represents the maximum
temperature of each compound during mixing and kneading. C/B means
carbon black.)
TABLE 4 ______________________________________ Tb Eb Permanent
Hardness (M Pa) (%) set Tan .delta.
______________________________________ Comparative Example 1 64
28.4 490 100 100 Comparative Example 2 64 26.5 460 98 98
Comparative Example 3 65 26.5 450 99 105 Comparative Example 4 65
28.9 515 96 102 Comparative Example 5 69 29.4 520 91 102
Comparative Example 6 64 28.4 490 97 101 Example 1 67 29.4 510 98
103 Example 2 71 29.4 520 95 102 Example 3 71 29.4 520 95 101
Example 4 73 29.4 515 98 101 Example 5 74 29.4 510 98 102 Example 6
74 28.9 510 98 101 Example 7 73 28.9 505 99 101 Comparative Example
7 82 27.5 400 * 98 Comparative Example 8 65 26.5 520 89 101
Comparative Example 9 66 27.5 515 89 101 Comparative Example 10 66
26.5 515 91 101 Comparative Example 11 67 27.5 510 91 101 Example 8
67 27.9 505 95 100 Example 9 69 27.9 495 96 107 Example 10 72 29.4
520 98 107 Example 11 75 27.9 490 98 103 Comparative Example 12 79
27.0 460 48 100 Example 12 82 27.9 465 55 100
______________________________________ * As described previously,
the sample had to be deformed up to 400%. Before that point the
sample has broken and thus the measurement of permanent set was
impossible.
Comparative Example 1 is an example in which polyisoprene is used
as the rubber component and no polyethylene resin is mixed at all.
This example was used as a control for evaluating physical
properties.
When Comparative Example 6 is compared with Examples 1-7, it is
found that when the polyethylene content of a rubber composition is
small, its hardness and Eb are low and that improvement effects
over Comparative Example 1 cannot be obtained. When Comparative
Example 7 is compared with Example 12, it is shown that when the
polyethylene content exceeds 75% by weight, Eb decreases
drastically and the balance among physical properties (hardness,
Tb, Eb) is lost. Further, it is found that even if the ratio of a
crosslinkable polyethylene is varied, an excellent performance is
obtained as long as the ratio falls within the range specified by
the present invention. Comparative Example 12 and Example 12
represent a system with a large polyethylene content. In these
examples, it is also seen that physical properties are improved by
the addition of a crosslinkable polyethylene.
When Comparative Examples 2 and 3 are compared with Examples 8 and
9, it is found that similar tendencies are also observed even if
the matrix rubbers are different.
From Example 10, it is seen that the replacement of a part of
carbon black with polyethylene is advantageous from the viewpoint
of the compatibility of Tb with small ten d . From Example 11, it
is seen that failure characteristics will be affected unless the
temperature of the kneaded compound is not higher than the melting
point of the polyethylene resin by 10.degree. C. or more.
Comparative Examples 4, 5, 8 and 9 are examples in which a
crosslinkable polyethylene is not used. In Comparative Example 4,
although resistance to the permanent set is not bad, hardness is
not improved. In Comparative Example 5, although hardness is
improved, resistance to the permanent set is bad. In Comparative
Examples 8 and 9, both hardness and resistance to the permanent set
are not good.
Although a crosslinkable polyethylene is mixed in Comparative
Examples 10 and 11, a low density polyethylene is also contained.
Therefore, they are inferior to Examples 5-7 in both hardness and
resistance to the permanent set.
As is clear from the results shown in Table 4, Examples 1-12
satisfying the conditions of the present invention are rubber
compositions in which the coexistence of low heat build-up, heat
resistance, high hardness and resistance to the permanent set can
be achieved without damaging failure characteristics.
On the other hand, in those rubber compositions as shown in
Comparative Examples 1-12 which do not satisfy all of the
conditions of the present invention, at least one of the following
properties of failure characteristics, low heat build-up, heat
resistance and high hardness become worse.
EFFECT OF THE INVENTION
According to the present invention, a rubber composition comprising
a 100 parts by weight of matrix rubber and a 2-75 parts by weight
of a polyethylene composition which contains 0-80% by weight of
polyethylene and 20% by weight or more of a composite comprising a
polyethylene component and a rubber component previously bonded via
a coupling agent to the polyethylene component, wherein the rubber
component is crosslinked with the matrix rubber improves the
dispersion of the polyethylene into the matrix rubber composition
and raises the interaction at interfaces between the polyethylene
and the matrix rubber, to thereby allow the coexistence of low heat
build-up, heat resistance, high hardness and resistance to the
permanent set without damaging failure characteristics.
* * * * *